I learned about JK a few months before it came out, sometime during the mid-late summer of 1997. I can't remember how exactly, it was probably by accident while I was looking for another mouthful of Dark Forces user-made levels to play (I was downloading them by the dozens a week at one point). I remember eventually finding out that the minimum system requirements were higher than anything I had at the time (Pentium 75Mhz, 16MB RAM, no video card) so, somewhat bummed, I didn't buy it when it came out figuring there wasn't much of a point. A friend at school loaned me his copy in November or December and I decided to see if I could actually play it. Turns out I could! It was frustratingly sluggish at times and levels took minutes to load but when I blasted that first duo of Gran and the bartender told me to hit the trail for always causing trouble, I couldn't have cared less. Dark Forces had let me walk around in the Star Wars universe, and now JK let me do it in 3D with tons more content. What more could I have asked for!?
My first experience with multiplayer was just playing over a direct modem-to-modem connection with a friend from school. I remember Jeff Walter's Carida map (anyone remember that one with the flying carpet?), which we thought was the best thing ever. Eventually I got around to playing internet games too.
I had never heard of MotS until I saw it in stores one day in March of '98. It rocked too. That same month my parents bought a Pentium 233Mhz w/ MMX, 48MB RAM computer that I added a 3dfx card to during the summer, so I wasn't stuck in slow, blurry 320x240 forever.